1. Field of the Invention
The present invention relates to a planar waveguide-type optical amplifier switch which is an optically lossless small switch using optical gain materials directly for the optical switch waveguide along with optical pumping. The present invention provides a solution for the problems occuring in the prior art of optical switches in which the loss of light occurs and the volume of the switch gets larger because an additional optical amplifier is required for compensating the loss of light occurring in conventional optical waveguide-type switch elements used in optical systems such as an optical transmission, an optical distribution system, an optical exchange, and an optical signal processing.
2. Description of the Prior Art
A conventional waveguide-type optical switch used in an optical communication system requires an external optical amplifier to compensate the loss of light and thus is not suitable for an integrated system device in a small compact form. It is therefore an object of the present invention to solve the problem of the optical loss related to the prior art of waveguide-type optical switches and to provide a waveguide-type optical amplifier switch that can be formed in a simply integrated device by using an optical material with an optical amplifying characteristic for the waveguides and by inducing optical amplification of the switched optical signals under an optical pumping.
The present invention is applicable for a key device in optical communication systems, optical switching systems, optical amplifiers, and optical signal processing.
In the prior art there are several technologies, such as electrically controllable optical switches using an electro-optic effect, electrically controllable optical switches using a thermo-optic effect, optically controllable optical switches using an optical control beam, waveguide-type optical amplifiers using an optical pumping, and so on.
Detailed descriptions on the above mentioned prior art will be described referring to the drawings of FIG. 2 to FIG. 5.
In the drawings of FIG. 2 to FIG. 5, the numeric 1 represents a wavelength division multiplexing (WDM) optical coupler, the numeric 2 represents a fluorescence emitting ion-doped waveguide, the numeric 3 represents an electrically controllable refractive index varying electrodes, and the numeric 5 represents a general optical waveguide respectively. And Lxe2x80x3 represents a waveguide coupling length.
FIG. 2 is a schematic diagram of a conventional planar waveguide-type optical amplifier that does not have a function of optical switch. [Y. Yan and A. J. Faber (EP 0867985), G. E. Blondee et al. (U.S. Pat. No. 5,039,190), Y. C. Yan et al. (Applied Physics Lett., Vol. 71, No 20, pp. 2922-2924, 1997)]. This structure has a defect that it can not provide a switching function because of the lack of an optical switch function in itself.
FIG. 3 is a schematic diagram of a conventional 2xc3x972 electrically controllable planar waveguide-type optical switch that does not have a function of optical amplification. [W. T. Bourd, et al. (U.S. Pat. No. 4,759,595), H Okayama and M. Kawahara (J. Lightwave Technol, Vol. 11, No, 2, pp. 379-387, 1993)]. This structure has a defect that it additionally requires an external optical amplifier to compensate for the loss of the light occurring in an optical switch.
FIG. 4 is a schematic diagram of a conventional 2xc3x972 optically controllable planar waveguide-type optical switch that does not have a function of optical amplification. [M. J. F. Digonnet, et al., (U.S. Pat. No. 5,920,666)]. This structure, likewise the structure in FIG. 3, has a defect that it additionally requires an external optical amplifier to compensate for the loss of the light occurring in the optical switch.
FIG. 5 is a schematic diagram of a conventional electrically controllable planar waveguide-type optical switch using Mach-Zehnder interferometer, that does not have a function of optical amplification. This structure, likewise the structure in FIG. 3, has a defect that it additionally requires an external optical amplifier to compensate the loss of the light occurring in an optical switch.
That is, because the optical switches of the above mentioned second prior art to the fourth prior art have only the switching functions but have no amplifying functions, they require external optical amplifiers to compensate for the loss of the light occurring in the optical switches, and thereby have difficulty being formed into a compact integrated device. To solve this difficulty or problem, the present invention provides a structure of constituting a waveguide of an optical material that has a characteristic of optical gain to provide an optical amplification function to the switch itself.
Since the waveguide-type optical amplifier using an optical pumping described in the first prior art has only an amplifier but has no switching function, the present invention provides a waveguide amplifier structure having an optical switching function together.
In other words, because the optical switches of the above mentioned second prior art to the fourth prior art have only the switching function without amplifiers and the waveguide-type optical amplifier described in the first prior art has no switching function, there is a defect that, when these devices are being used, each of them should be fabricated independently and be combined to be used, thereby they can not be integrated into a simple compact device. The technical aspect of the present invention is to solve above mentioned problem of the loss of light that had existed in the conventional optical switches and thereby to provide an optical switch element that is more practical and is capable of being integrated in a compact lossless device.
A number of other prior arts includes (1) optical coupler type optical switches composed of active ion doped waveguides with pump controlled differential gain adjustment, [K. J. Blow (U.S. Pat. No. 5,583,957), M. Shigematsu, and K. Nakazato (U.S. Pat. No. 5,136,670)], (2) semiconductor based optical waveguide switches utilizing current-injected gain differences in a gain-guided channel or utilizing voltage-controlled refractive index change and control light absorption wavelength [M. Fujiware (U.S. Pat. No. 4,778,235), S. Nakamura (U.S. Pat. No. 5,329,601), N. Susuki (U.S. Pat. No. 5,754,714)], (3) thermo-optic waveguide switches utilizing a large temperature gradient on heating [N. Ooba, e al. (U.S. Pat. No. 6,122,416)], and (4) wavelength selective optical swithes utilizing grating assisted mode coupling [A. S. Kewitsch, et al. (U.S. Pat. No. 5,875,272)]. Among these prior arts the first and second types of switches can provide optical switching along with optical amplification during the switching functions, but they use different mechanisms from our invention. Operating speed of the first type optical switches are limited by the speed of the pump power change which may not be so fast as that of an all-optical switch using a separate high-speed control light injection just like the one proposed by our invention. The second type of optical switches are optical control type optical switches utilizing voltage applied optical absorption spectrum shifts or utilizing electrical current injected optical gains, while our invention uses optical pumped waveguide gain and optical control type optical switching. The latter two types of the prior arts have only switching mechanisms without optical signal amplification, which are different from our invention. Our invention also proposes potential high-speed optical control optical switches combined with an optical signal amplification function.
It is therefore an object of the present invention to provide a planar waveguide-type optical amplifier switch intended to solve the problems that the prior art have.
To achieve the object, the present invention amplifies an optical signal passing through a switch waveguide by performing an optical pumping through a wavelength division multiplexing optical coupler into the optical waveguide comprising a fluorescence emitting material, and at the same time, carries out an optical switching by using an optical waveguide refraction index change under an electrical control.
The present invention provides a waveguide-type optical amplifier switch, that carries out the function of amplifying the optical signal under an optical pump in co-propagating direction to the signal input and the function of switching the signal light simultaneously, and consists of a 2xc3x972 optical coupler using an optical waveguide of a fluorescence emitting material; one or two input signal terminals; two output signal terminals; two electrically controllable electrodes that are located upon each waveguide corresponding to the coupling area of the coupler; two 2xc3x971 or 2xc3x972 wavelength division multiplexing optical waveguide couplers whose arms are installed upon the two input waveguides of the 2xc3x972 optical coupler respectively to make the pump light propagate to the same direction as that of signal light; an input terminal for a pump light; and a Y-type optical power splitting waveguide that leads the divided pump lights by the power splitter to pass through a wavelength division multiplexing optical coupler and to incident to the input terminal of the 2xc3x972 optical coupler.
The present invention also provides a waveguide-type optical amplifier switch, that carries out the function of amplifying the optical signal under an optical pump in counter-propagating direction to the signal input and the function of switching the signal light simultaneously, and consists of a 2xc3x972 optical coupler using an optical waveguide of a fluorescence emitting material; one or two input signal terminals; two output signal terminals; two electrically controllable electrodes that are located upon each waveguide corresponding to the coupling area of the coupler; two 2xc3x971 or 2xc3x972 wavelength division multiplexing optical waveguide couplers whose arms are installed upon the two output waveguides of the 2xc3x972 optical coupler respectively to make the pump light propagate in the reversed direction to the signal light; an input terminal for a pump light source; and a Y-type optical power splitting waveguide that leads the divided pump lights by the power splitter to pass through a wavelength division multiplexing optical coupler and to incident to the output terminal of the 2xc3x972 optical coupler.
The present invention also provides a waveguide-type optical amplifier switch, that carries out the function of amplifying the optical signal under optical pump in co-propagating direction to the signal input and the function of switching the light simultaneously, and consists of a 2xc3x971 or 2xc3x972 wavelength division multiplexing optical waveguide-type coupler that is installed upon the input terminal side to make the pump light propagate to the same direction as that of signal light; input and output signal terminals; a pump light input terminal connected to the wavelength division multiplexing optical coupler; a Y-type 1xc3x972 optical divider and a Y-type 2xc3x971 optical coupler, both of which have an optical signal distributing function in the pump light and signal light; a pair of waveguides that constitute Mach-Zehnder interferometer by connecting the two arms of both the Y-type 1xc3x972 optical divider and Y-type 2xc3x971 optical coupler; and electrically controllable electrodes that are located upon the two arms of the pair of waveguide in pairs or upon one of the two arms of the pair.
The present invention also provides a waveguide-type optical amplifier switch, that carries out the function of amplifying the optical signal under optical pump in counter-propagating direction to the signal input and the function of switching the light simultaneously, and consists of a 2xc3x971 or 2xc3x972 wavelength division multiplexing optical waveguide-type coupler that is installed upon the output terminal side to make the pump light propagate to the reverse direction with respect to the signal light; input and output signal terminals; a pump light input terminal connected to the wavelength division multiplexing optical coupler; a Y-type 1xc3x972 optical divider and a Y-type 2xc3x971 optical coupler, both of which have an optical signal distributing function in the pump light and signal light; a pair of waveguides that constitute Mach-Zehnder interferometer by connecting the two arms of both the Y-type 1xc3x972 optical divider and Y-type 2xc3x971 optical coupler; and electrically controllable electrodes that are located upon the two arms of the pair of waveguide in pairs or upon one of the two arms of the pair.
The present invention also provides a waveguide-type optical amplifier switch, that amplifies an optical signal passing through the waveguide under an optical pumping coupled through a wavelength division multiplexing optical coupler into the optical waveguide comprising a fluorescence emitting material, and at the same time, carries out an optical switching by using an optical waveguide refraction index change under an optical control.
The present invention also provides a waveguide-type optical amplifier switch, that carries out the function of amplifying the optical signal under optical pump in co-propagating direction to signal input and the function of switching the light simultaneously, and consists of a 2xc3x972 optical waveguide-type coupler made of a fluorescence emitting material; one or two input signal terminals; two output signal terminals; two 2xc3x971 or 2xc3x972 wavelength division multiplexing optical waveguide-type couplers that are installed upon the two input waveguides of the 2xc3x972 optical coupler respectively to make the pump light propagate to the same direction as that of signal light; and two input terminals for pump light source.
The present invention also provides a waveguide-type optical amplifier switch, that carries out the function of amplifying the optical signal under optical pump in counter-propagating direction with respect to the signal input and the function of switching the light simultaneously, and consist of a 2xc3x972 optical waveguide-type coupler made of a fluorescence emitting material; one or two input signal terminals; two output signal terminals; two 2xc3x971 or 2xc3x972 wavelength division multiplexing optical waveguide-type couplers that are installed upon the two output waveguides of the 2xc3x972 optical coupler respectively to make the pump light propagate to the reverse direction with respect to the signal light travel; and two input terminals for pump light source.